The invention relates to communications systems and methods, and more particularly to a system and method for wireless communications using bandwidth of a cable network.
Because of the popularity of cable television (CATV), cable networks for transporting CATV signals to CATV subscriber premises proliferate at a rapid pace. Taking advantage of the broad band provided by a cable network, telephone companies deliver wireless telephony services, e.g., a personal communications service (PCS), through the network. For example, the cable network affords a communication medium between a base station and cable microcell integrators (CMIs) connected thereto for providing the PCS. A CMI is typically mounted on a cable trunk in the cable network, and includes antennas for transmitting and receiving in a wireless manner communication information to and from mobile terminals, e.g., radiotelephones, subscribing to the PCS. The base station performs call administration, and establishes and maintains telephone connections between the mobile terminals and other communication terminals, which may or may not be mobile terminals, via, e.g., a public switched telephone network (PSTN).
After a telephone connection is established between a communication terminal and a mobile terminal, the base station generates a transmit signal representative of digital information from the communication terminal, in accordance with the PCS standard and a well known multiple access technique, e.g., a code division multiple access (CDMA) technique. The base station sends the transmit signal, through a forward cable band (450 MHz-750 MHz) provided by the cable network, to the CMIs where the digital information is transmitted to the mobile terminal. In the reverse direction, the CMIs receive digital information from the mobile terminal, and send multiple reverse PCS CDMA signals containing the received information, through a return cable band (5 MHz-42 MHz) provided by the cable network, to the base station where the information is transmitted to the communication terminal, thereby realizing duplex communications.
Recently, a number of applications emerged, known as xe2x80x9creturn service applications,xe2x80x9d which need to also utilize the return cable band to provide, e.g., pay per view services, Internet access, interactive games, etc. Although the reverse PCS CDMA signals do not fully populate the 5 MHz-42 MHz return cable band, thus leaving unused bandwidth therein, the return service applications, however, cannot take advantage of such unused bandwidth as the whole return cable band is corrupted by broadband noise entering through the CMIs.
An effort has been made to make available bandwidth in the return cable band to accommodate the return service applications. This effort involves use of a bandpass filter to limit the band for the reverse PCS CDMA signals to only 5 MHz through 18 MHz, thereby affording the remaining return cable band 18 MHz through 42 MHz to the return service applications. However, such an effort is ineffective as the return service applications are accommodated at the expense of the PCS, thereby adversely affecting the PCS.
Accordingly, there exists a need for a methodology for effectively locating bandwidth in a return cable band of a cable network for return service applications, without adversely affecting the PCS.
I have recognized that because of use of the CDMA technique in the PCS described above, even though the reverse PCS communication is active, the power spectrum of the reverse CDMA PCS signals, including their power level, resemble that of pure channel noise as if no communication were going on. In other words, a pure-channel-noise-like signal, referred to as a xe2x80x9cpedestal noise signal,xe2x80x9d always appears in a signal band being used for the PCS in the return cable band, regardless of whether the reverse PCS communication is active. I have also recognized that the power level of the pedestal noise signal is significantly higher than that of the broadband noise corrupting the return cable band.
Thus, in accordance with the invention, the pedestal noise signal is detected to identify the signal band being used for the PCS. Such detection may be based on a significant rise in the power level in a transition from the broadband noise to the pedestal noise signal in the return cable band. A tunable filter is used, whose passband is controllably adjusted to cover the identified signal band, to filter out the noise in the rest of the return cable band.
Advantageously, with the invention, the bandwidth unused by the PCS in the return cable band, which is noise-free, can be allocated to the return service applications, without affecting the PCS.